First tournament

So I've never participated in one before and I'm not really sure how they work. My first question is which is the best one to join and my second is how do tournaments effect your online rating? Thanks

1. Play a small tournament first time out. The big ones take a very long time, and may not be to your taste,

2. Almost all tournaments affect your rating, in the same way as any other set of games.

Thanks. Also, can you play in the app?

I agree with Doggy and I should add some other things to consider.  First,  days per move.  Second, rating range.  If you want to use Online Tournaments to improve, then these two points are crucial.  Are you more comfortable with 5-day, 3-day or faster?  Also, there are plenty of narrow range tournaments on this site.  It just takes a lot of searching the Tournaments List to find one that suits you.  Keep clicking pages until you find one you feel comfortable with.

Thanks for the info guys